Thoroughbreds are know to have a number of white spotting
patterns (formerly called dominant white or extreme sabino)with
a range of expressions. At one time, these patterns were thought to be
the result of sabino, but interestingly, no white patterned Thoroughbreds
have been found to carry Sabino-1. White spotting (W) is family of spontaneous
mutations of the KIT gene--- this is why white horses crop up from seemingly
ordinary, solid-colored parents. Twenty W-mutations have been identified
to date (2015), six of which originate in Thoroughbreds, and one more
seems to be wide-spread, including in Thoroughbreds. They are:

W2: KY Colonel line which gave rise to the well-known
Patchen Beauty family

W5: Puchilingui line

W6: Unidentified white TB born in 2004 (possibly Marumatsu
Live)

W7: Unidentified white TB born in 2005 (I suspect it
must be Turf Club)

W12: Unidentified white TB

W14: Shirayukihime line

W20: May be responsible for what we think of as "normal"
markings (socks, blazes, etc). Has been found in conjunction with other
W-mutations, and seems to act as a white-booster.

White spotting patterns vary in expression. Puchilingui's family tends
to produce horses that are a mix of their base color and white. Horses
from the Patchen Beauty and Shirayukihime lines tend to produce horses
that appear all white. (Most do still have some spots of dark color
in their ears or along their top line.)

The incredible Puchingui, founder of the W5 line. (Photo by
Dan Trout)

This is The White Fox, a son of Patchen Beauty and part of the
W2 family.

Click here for more information on the myths and
facts about "white" horses. More pictures of pinto TBs can be found
here.

There are a variety of Thoroughbreds who fit the white
spotting template but whose W-mutations have not yet been identified.
These include Not Quite White (dam of Airdrie Apache), Our White Lady,
The Opera House, etc. As with the identified W-mutations, a range of
expression is found in the unidentified but presumed W-families as well.
Airdrie Apache's family in particular tends to produce partially white
and all white horses, suggesting that it may be a W-pattern that is
boosted when combined with another W-mutation.

Airdrie Apache is a son of the nearly all white mare Not Quite White.
The W-mutation for this family has not yet been identified. He was bred
and owned by Painted Desert Farm.

Arctic White, a son of Airdrie Apache.

Thoroughbreds with loud markings like wide blazes and tall socks have
been found in the breed since its inception. The Darley Arabian, perhaps
the most influential of the Arabian foundation stallions, was himself
a boldly marked bay. Northern Dancer is an example of a well-known modern
source of bold markings in Thoroughbreds. For a long time, these markings
were thought to be the result of sabino, but recent genetic testing has
forced us to rethink that.

The Darley Arabian, one of the founding sires of the Thoroughbred.

The great sire Northern Dancer has long been a source of big
blazes and tall socks.

The
lovely stallion Marquetry who had fascinating markings. (Photo
by Tony Leonard)

Frame Overo

The frame overo pattern does exist in the Thoroughbred gene
pool, but it is limited to only a handful of family lines. The only
frame overo TBs I know of have cropped up in the last 20 years. All
are from relatively obscure lines, and the presence of the pattern may
be due to a random mutation.

In TBs, frame is almost always seen in conjunction with the sabino
pattern which makes for some spectacularly patterned horses. Horses
carrying only the overo gene often have four dark legs. White legs on
a horse also carrying frame overo usually indicates sabino or another
white pattern at work.

The first frame TB I'm aware of is Tri Chrome (shown
with trainer Jack Van Berg), a bay overo horse by Blue Gazi born in 1991.
Sadly, he was euthanized at a young age after being kicked in the paddock
before a race. He was never bred.

This is Blue-Eyed Streaker, a 1993 bay overo stallion, also
a son of Blue Gazi. He currently stands at Echo
Hill Farm.

If anyone has a picture of Blue Gazi, I would very much like to see
it. Thanks!

And this is alleged to be Fillipas Puzzle(Great
Deal x Phillipes Doll, by My Phillipe), a 1993 bay overo mare who
is truly a puzzle. Her whereabouts are unknown, and she has no known progeny.
Any further information on her would be greatly appreciated.

The most prolific family of frame overo TBs stems from the pairing
of two "half" siblings, Pesty Axe and Torchy's Rainbow, both
by Give Em The Axe. They produced two foals, Nite Spot in 1985 and Patchy
Lassy in 1989. Nite Spot is a boldly marked bay frame overo, and his
sister is a chestnut with a big blaze and tall stockings.

Patchy Lassy, shown here with her 2000 colt Ellusive
Quest, is a minimaly expressed overo (presumably). Quest's frame pattern
is probably boosted by some version of white spotting. (Both horses
are owned and photographed by Nancy McEachern of Color
World Ranch.)

The late, great Racey Remarque, a 1997 black frame
overo son of Patchy Lassy. Thankfully, he sired some lovely overo foals
before his untimely death. (Owned and photographed by Nancy McEachern
of Color World Ranch.)

Is this guy something or what? He is the very handsome Ellusive
Quest (as pictured above with Patchy Lassy), a full brother to Racey
Remarque. He had a brief racing career, but was retired to stud when his
brother died. (Owned and photographed by Nancy McEachern of Color
World Ranch.)

Splash White

The splash white overo pattern has only recently been
recognized in the Thoroughbred. Though there have been a few isolated
reports of potential splash whites, no good examples were found until
a mare named Hey What The in New Zealand produced two unique fillies in
2003 and 2004. As with the frame pattern, the origins of splash in TBs
are mysterious. In heterozygous form, splash can be very minimal,
as little as a small snip on the nose, so it may have flown under the
radar, so to speak, or it my be the result of a spontaneous mutation.

This is Hey What The, a bay splash 1998 mare by Hey
Baba Riba (NZ) out of Nagol Lass (NZ), by Americus (IRE), pictured with
her 2004 filly Bubba by Go Corp (NZ). Hey What The is currently
owned by Massey Farms; Bubba
unfortunately was euthanized in 2008.

Here are Hey What The and Bubba again showing
off their white tail tips, classic indicators of splash. And though you
can't see it in these photos, HWT has a big white belly spot as well.

This is Hey What The with her 2003 filly Whatever
also by Go Corp (NZ). Whatever is currently owned by Painted
Fox Horses.

These odd patterns of dark and light spots do occur in other breeds,
but they seem to be particularly prolific in the Throughbred, and many
of them are actually named after TBs. The genes responsible for these
spots have not yet been identified, so not a great deal is known about
them.

Birdcatcher spots or ticks are patterns
of small white spots on a dark coat. Usually, these spots appear once
a horse has reached maturity and eventually disappear. Sometimes, however,
they do seem to be permanent. This is Willspynow, a 1991 mare by Well
Selected out of Spy Gail, by Father Hogan. This mare's spots are bigger
and more highly concentrated than most Birdcatcher spots. (Photo by
Barbara Livingston)

Chubari spots (also sometimes called Tetrarch
spots) are similar to Birdcatcher spots except that they tend to be
much larger. They are usually egg-shaped and egg-sized, as seen here on
The Tetrarch. They seem to be tied to the grey color, but they are different
from dapples. Dapples can change and fade as the horse ages, but chubari
spots don't disappear until the horse has completely greyed out. Many
grey TBs have a few chubari spots but it is unsual to see a horse with
as many as The Tetrarch.

Bend Or spots are random dark spots on a horse's
coat. Man O' War, a descendant of Bend Or, is said to have had these spots.
Pictured at left is Commendable, the 2000 Belmont winner, who has a Bend
Or spot on his right hip. Bend Or spots seem to show up most frequently
on chestnuts and chestnut-based colors, like palomino, but they can occur
on other colors. (Photo by ?)

This pattern is known as manchado or "manchado overo."
It has only cropped up in Argentina in a handful of horses from various
breeds (Criollo, Hackney, Arab, and TB so far). Little is known about
manchado at the moment, but it may be an exceedingly rare recessive
gene. The pattern is not known to be related to other spotting patterns
like the appaloosa pattern or Bend Or spots. The horse pictured is a
Thoroughbred, Royal Manchado, a 1990 stallion by Royal Castle
(ARG) out of Kleymary (ARG), by Manchester (ARG).

(As a sidenote, here is a photo of the manchado purebred Arab mare
Trabag
born in 1946. She did not pass her pattern on to any of her foals.)

Some spots are the result of environmental factors rather than genetic
ones. Pelouse's Queen (Pelouse x Harem Queen, by Nathoo), a 1965
dark bay Thoroughbred mare, was so afflicted by a skin disease that
her coat grew back in white where it had been scarred by the fungal
infection. She was purchased by an Appaloosa breeder, but as she did
not of course carry the leopard complex (not found in TBs), she could
not pass on the color.